Data packets arriving from a network are usually placed into a buffer queue to be processed by a host computer. When and how often an interrupt signal needs to be generated to alert the host that there are data packets waiting in the queue is usually a compromise between latency (how long the data must wait in the queue before the host is notified) and performance (how often the host is interrupted--an interrupt can require considerable processing by the host). The existing technique of generating an interrupt for every data packet provides minimum latency but can overwhelm a slow host with a large number of interrupts.
Existing schemes generate an interrupt every packet. The card would generate an interrupt every time an end-of-packet buffer is enqueued to the host. This method provides minimum latency but can generate multiple interrupts per packet. Lots of interrupts can be generated for short packets and a slow host (worst combination).
Other existing methods use a counter or timer to limit the number of interrupts but can have latency problems especially for video or voice data. An interrupt is generated every N packet and M clock ticks from the time the last packet was enqueued. This method attempts to minimize the number of interrupt by generating an interrupt after N packets are enqueued (N is programmable). To minimize latence in case N is large, an interrupt is generated based on a timer. The timer is triggered at the end of a packet. If the timer crosses a M threshold (programmable) without detecting the end of another packet, then an interrupt is generated. Using this scheme requires the programming of two parameters: N and M. It is difficult for the host to determine the optimum value for N and M for different load conditions and variations of the host and card.
The present invention produces interrupt signals based on the speed the host can process data. The interrupt signals are sent at intervals which do not overwhelm the host and significantly effect performance.